Title

PU MP ASS EM BLY FOR SU PPLYI NG FU EL FROM A TAN K TO AN INTE RNAL COMBUSTION ENGIN E

The present invention relates to a pump assembly for supplying fuel, preferably diesel, from a tank to an internal combustion engine.

In particular, the present invention relates to a pump assembly comprising, in series, a low-pressure pump (or pre-supply pump) for drawing and initial compression of the fuel, and a high-pressure pump for further compression of the fuel and for supplying the fuel at high pressure to an internal combustion engine.

The use of systems for supplying fuel, in particular diesel, to an internal combustion engine, which comprise a high-pressure pump for supplying the internal combustion engine, and a low-pressure pump for supplying fuel to the high-pressure pump, is already known. The high-pressure pump comprises at least one pumping piston moved by a shaft and housed in a cylinder supplied with fuel at low pressure. At least two different types of low-pressure pump for such systems currently exist.

The first type comprises a gear pump which is driven by the same shaft as drives the pistons of the high-pressure pump. In particular, this gear pump may be a "gerotor" pump. As is known, the gerotor pump comprises an external spur rotor rotated by the shaft and housed inside an internal spur rotor. During rotation, the spurs of the external spur rotor engage with the spurs of the internal spur rotor, which has one more spur than the external spur rotor. The two rotors, rotating either absolutely or relatively, or relative to one another, pump fuel from an inlet, connected to the tank, to an outlet, connected to the high-pressure pump. The second type of gear pump comprises gear pumps not driven by the shaft for driving the pumping pistons, but pumps driven electrically or electromagnetically. With this type of pump, in gerotor pumps, at least one out of the internal spur rotor and the external spur rotor has magnetic modules, such as little plaques made of iron, which engage electromagnetically with a stator which is arranged outside the internal spur rotor and comprises electrical windings. By supplying current to said windings, electromagnetic conditions are created such that the gerotor starts to operate, pumping the fuel between the tank and the high- pressure pump.

The known pump assemblies in which a gerotor electric gear pump, described above, is installed have a number of drawbacks.

One such drawback is the fact that, after the gerotor electric gear pump is switched off, for example owing to an unforeseen and unwanted current failure or due to its being switched off temporarily to save energy while the vehicle is stopped, it is currently necessary to wait for a certain period of time before being able to restart the gerotor electric gear pump. Since the length of the wait is around a few seconds, but may in some cases exceed 10 seconds, this drawback is not only annoying but also dangerous in the case where it is necessary to get moving quickly in order to get away from a hazardous or potentially hazardous situation.

The technical reason behind this drawback is linked to the nature of the actual gerotor electric gear pump, as described above. To be specific, this type of pump may be started up after being switched off only if, across the pump itself, i.e. between the inlet connected to the low-pressure supply pipe connected to the tank and the outlet connected to the low-pressure delivery pipe connected to the high-pressure pump, there is a pressure difference which is below a threshold value, usually around 2 bar.

During use, downstream of the gerotor electric gear pump, the pressure, or counter-pressure, stands at a few bar, usually 8 bar. After the gerotor electric gear pump has been switched off, downstream thereof, the initial pressure mentioned above does not drop suddenly but falls slowly under the effect of the devices connected to said pipe, for example the relief valve, the calibrated or bypass holes, etc. During use, upstream of the gerotor electric gear pump there is a slight depression owing to the pull of the pump. Immediately after the gerotor electric gear pump is switched off, the fuel present in the supply pipe of said pump is spontaneously discharged into the tank. In such circumstances, i.e. in the absence of pressure upstream of the gerotor electric gear pump, the only way to achieve, across said pump, a pressure difference which is below the threshold value is by waiting for the counter-pressure downstream of the gerotor electric gear pump to fall, down to values which allow restarting.

The only solution which is currently feasible for reducing said waiting time is to increase the torque which can be delivered by bursts of rotation of the gerotor. However, this solution has drawbacks both in structural terms, as it feasible only with major motorizations, and in terms of production cost.

In light of the known prior art, it is an aim of the present invention to produce an alternative pump assembly for supplying fuel, preferably diesel, from a tank to an internal combustion engine.

In particular, it is an aim of the present invention to produce a pump assembly for supplying fuel, preferably diesel, from a tank to an internal combustion engine which makes it possible to overcome the drawbacks of the prior art described above, simply and economically, both from the functional viewpoint and from the structural viewpoint.

In accordance with these aims, the present invention relates to a pump assembly for supplying fuel from a tank to an internal combustion engine, in which the pump assembly comprises:

- a low-pressure electric gear pump;

- a high-pressure pump; - a low-pressure suction pipe for supplying the fuel from the tank to the low- pressure electric gear pump;

- a low-pressure delivery pipe for supplying the fuel from the electric gear pump to the high-pressure pump;

- at least one high-pressure delivery pipe for supplying the fuel from the high- pressure pump to the internal combustion engine;

- a selective obstruction device designed to obstruct the low-pressure delivery pipe, in an intermediate position between the electric gear pump and the tank, when the electric gear pump is switched off.

Advantageously, in this way, when the electric gear pump is switched off, the fuel in the low-pressure suction pipe, in particular in the section of said pipe downstream of the selective obstruction device, is prevented from being discharged into the tank. By thus retaining fuel, it is possible to increase the pressure upstream of the electric gear pump and hence reduce the pressure difference across said pump. By thus starting with a smaller pressure difference, the time to wait before being able to restart will necessarily be shorter since the fall required in the counter-pressure downstream of the electric gear pump will not be as great. For example, with a pressure of around 2 bar upstream of the electric gear pump, it is possible to restart as soon as a counter-pressure value of 4 bar is reached. There is thus a significant reduction in the waiting time with respect to the known prior art in which it is possible to restart only on reaching a counter-pressure value of 2 bar. The technical reason why, in the closed section of the low-pressure supply pipe, the abovementioned pressure of 2 bar is created is that in the electric gear pump, owing to its nature, there are clearances which lead, when the pump is closed, to drops in pressure from the downstream section to the upstream section.

In particular, according to a preferred embodiment of the invention, the electric gear pump comprises a gerotor and, preferably, the selective obstruction device is a valve.

Advantageously, the ideal increase in pressure in the closed section of the low- pressure supply pipe is thus ensured.

According to two alternative embodiments of the invention, the valve may be a solenoid valve connected to the electric gear pump or a non-return valve designed to inhibit the flow from the electric gear pump to the tank.

In the case of a solenoid valve, the command to close the low-pressure supply pipe may be given rapidly by a control unit which can electronically detect that the electric gear pump has been switched off.

In the case of a non-return valve, the low-pressure supply pipe is closed spontaneously in the absence of current.

According to two alternative embodiments of the invention, the non-return valve is arranged approximately half way along the length of the low-pressure delivery pipe or is arranged in the half of the low-pressure delivery pipe next to the electric gear pump.

Further features and advantages of the present invention will become clearer from the description below of a non-limiting embodiment thereof, with reference to the figures in the attached drawings, in which:

- Figure 1 is a schematic view of an embodiment of a pump assembly according to the known prior art for supplying fuel, preferably diesel, from a tank to an internal combustion engine, which comprises, in series, a low-pressure pump and a high-pressure pump;

- Figure 2 is a schematic view of a low-pressure gerotor gear pump which may be operated electronically;

- Figure 3 shows a diagram with the pressure (in bar) and the time (in seconds), showing the evolution over time of the pressure downstream of the low-pressure pump forming part of the assembly of Figure 1, after switching off, until it reaches the conditions for restarting;

- Figure 4 is a schematic view of an embodiment of a pump assembly according to the present invention for supplying fuel, preferably diesel, from a tank to an internal combustion engine, which comprises, in series, a low-pressure pump and a high-pressure pump;

- Figure 5 shows a diagram with the pressure (in bar) and the time (in seconds), showing the evolution over time of the pressure downstream of the low-pressure pump in the assembly of Figure 4, after switching off, until it reaches the conditions for restarting; for a visual comparison, the diagram of Figure 3 is superposed thereon.

There follows below a detailed description of the figures which, as mentioned above, are simply examples of embodiments of the invention.

Figure 1 is a schematic view of an embodiment of a pump assembly according to the known prior art for supplying fuel, preferably diesel, from a tank to an internal combustion engine, which comprises, in series, a low-pressure pump and a high- pressure pump. In particular, Figure 1 shows a pump assembly comprising:

- a low-pressure electric gear pump 4;

- a high-pressure pump 5;

- a low-pressure suction pipe 6 for supplying the fuel from the tank 2 to the electric gear pump 4;

- a low-pressure delivery pipe 7 for supplying the fuel from the electric gear pump 4 to the high-pressure pump 5;

- high-pressure delivery pipe 8 for supplying the fuel from the high-pressure pump 5 to the internal combustion engine 3.

In this example, the internal combustion engine 3 is shown only schematically and comprises a common manifold 17 fed by the high-pressure delivery pipes 8 and a plurality of injectors 18 (not shown) designed to spray and inject the fuel at high pressure into the cylinders of the internal combustion engine 3. In Figure 1, the high-pressure pump 5 is shown only schematically and comprises two pumping pistons 11 supplied with fuel at low pressure at supply valves 12 and connected to delivery valves 13 for supplying the fuel at high pressure to the engine 3. Figure 1 also shows a filter 10 arranged downstream of the low- pressure pump 4, a fuel measuring device 14 downstream of the filter 10, a relief valve 15 between the filter 10 and the fuel measuring device 14, a pressure limiting valve 26 connected to the manifold 17 and a valve 28 for delivering to the tank 2. The arrows shown in Figure 1 indicate the path of the fuel through the pump assembly 1, while the arrow in dashed lines represents the fact that, when the low-pressure pump 4 is deactivated, the fuel present in the low-pressure supply pipe 6 is spontaneously discharged into the tank 2.

Figure 2 shows a type of low-pressure pump 4, in particular a gerotor electric gear pump 19. As shown in Figure 2, said gerotor 19 comprises an internal spur rotor 20, inside which is housed an external spur rotor 21. As is known, the gerotor 19 comprises an inlet 22, connected to the low-pressure supply pipe 6, and an outlet 23 connected to the high-pressure delivery pipe 7. Figure 2 schematically shows the chambers inside the gerotor 19 for supply, at the inlet 22, and for delivery, at the outlet 23. The way in which the gerotor 19 operates is known.

Figure 3 shows a diagram with the pressure (in bar) and the time (in seconds), showing the evolution over time of the pressure at the outlet of the gerotor 19, which is understood to constitute the low-pressure pump 4 of the assembly of Figure 1. In particular, the first portion of the diagram shows the pressure over time at the outlet 23 of the gerotor 19 during normal use of the assembly of Figure 1. In this portion, the pressure is constant and stays at around 8 bar. After little more than a second, the low-pressure pump 4 is switched off and this leads to gradual lowering of the pressure down to the value of 2 bar, at which it is possible to restart the pump 4. To be specific, when these conditions are in place across the pump 4, there is a pressure difference of less than or equal to the threshold value for restarting, namely 2 bar. In this example, the waiting time before being able to start the pump 4 is around 2.5 seconds, while the operating mode is not reached until 3.3 seconds after the pump 4 is switched off.

Figure 4 is a schematic view of an embodiment of a pump assembly according to the present invention for supplying fuel, preferably diesel, from a tank to an internal combustion engine, which comprises, in series, a low-pressure pump and a high-pressure pump.

With respect to the pump assembly of Figure 1, the pump assembly of Figure 4 further comprises a selective obstruction device 9 designed to obstruct the low- pressure delivery pipe 7, in an intermediate position between the electric gear pump 4 and the tank 2, when the electric gear pump 4 is switched off. In particular, in Figure 4 this selective obstruction device 9 takes the form of a nonreturn valve 16 designed to automatically inhibit the flow of fuel from the electric gear pump 4 to the tank 2 which happens spontaneously when the electric gear pump 4 is switched off. The inhibition of this return flow of fuel is shown schematically in Figure 4 by a barred arrow.

Figure 5 shows a diagram with the pressure (in bar) and the time (in seconds), showing the evolution over time of the pressure at the outlet 23 of the electric gear pump 4, or a gerotor 19, of the assembly of Figure 4. In particular, the first portion of the diagram shows the pressure over time at the outlet 23 of the gerotor 19 during use of the low-pressure pump 4. In this portion, the pressure is constant and stays at around 8 bar. After little more than a second, the low- pressure pump 4 is switched off and this leads to gradual lowering of the pressure down to the value of 4 bar, at which it is possible to restart the pump 4. Indeed, by virtue of the non-return valve 16 a pressure of around 2 bar is created upstream of the gerotor 19, and hence the pressure difference of 2 bar across the gerotor 19 is reached when the counter-pressure reaches the value of 4 bar. With the present invention, under the same conditions as the assembly of Figure 1, the waiting time before the assembly of Figure 4 can be restarted is around 0.4 seconds, while the operating mode is reached after only 0.8 seconds. Comparing the diagrams relating to the known assembly of Figure 1 and the new assembly of Figure 4, it is clear that, with the present invention, there is a saving of time of around 2.5 seconds which reduces the waiting time from 3.3 seconds to 0.8 seconds.

Lastly, it is clear that amendments and variations may be made to the invention described herein without exceeding the scope of the attached claims.